If I understand your description correctly, the magic( ) function has nothing to do with your assignment. You are simply asked to construct an m x n matrix where the (i,j) element has the value i+j. That's it, nothing else. So an outline:
function A = MagicArrayAdd(m,n)
A = ____;
Fill in the blanks above.
To create the matrix, you could e.g. use the zeros( ) function.
For the i+j stuff, you could use two nested for-loops over the elements of A, or you could use vectorized code, etc.